lf-tide emotion, but the
full-tide manifestation of an emotion which dominates the situation, we
are naturally led on to the consideration of many of the phenomena
which are discussed under the head of sexual selection. The subject
is difficult and complex, and it was treated by Darwin with all the
strength he could summon to the task. It can only be dealt with here
from a special point of view--that which may serve to illustrate the
influence of certain mental factors on the course of evolution. From
this point of view too much stress can scarcely be laid on the dominance
of emotion during the period of courtship and pairing in the more highly
organised animals. It is a period of maximum vigour, maximum activity,
and, correlated with special modes of behaviour and special organic and
visceral accompaniments, a period also of maximum emotional excitement.
The combats of males, their dances and aerial evolutions, their
elaborate behaviour and display, or the flood of song in birds, are
emotional expressions which are at any rate coincident in time with
sexual periodicity. From the combat of the males there follows on
Darwin's principles the elimination of those which are deficient in
bodily vigour, deficient in special structures, offensive or protective,
which contribute to success, deficient in the emotional supplement
of which persistent and whole-hearted fighting is the expression,
and deficient in alertness and skill which are the outcome of the
psychological development of the powers of perception. Few biologists
question that we have here a mode of selection of much importance,
though its influence on psychological evolution often fails to receive
its due emphasis. Mr Wallace ("Darwinism", pages 282, 283, London,
1889.) regards it as "a form of natural selection"; "to it," he says,
"we must impute the development of the exceptional strength, size, and
activity of the male, together with the possession of special offensive
and defensive weapons, and of all other characters which arise from
the development of these or are correlated with them." So far there is
little disagreement among the followers of Darwin--for Mr Wallace,
with fine magnanimity, has always preferred to be ranked as such,
notwithstanding his right, on which a smaller man would have constantly
insisted, to the claim of independent originator of the doctrine of
natural selection. So far with regard to sexual selection Darwin and Mr
Wallace are agreed